Numerous techniques have been proposed for producing thermally cellulated bodies from such diverse materials as glasses, ceramics and organic plastics. It is customary to introduce a source of gas, either in a parent batch or in a granular mixture of the prepared material. Such known cellulated products are generally intended to be durable and resistant to attack.
The cellulated materials of the present invention find particular application in low temperature casting of organic plastics and soft metals at temperatures up to 500.degree. C. However, they may also be useful in casting other molten materials, such as glasses and metals, at higher temperatures.
It is common foundry practice to employ sand molds in casting molten metals, such as iron. Such molds are composed essentially of sand grains mixed with an organic binder, such as pitch. The binder burns out during casting, and the mold readily breaks away from the casting.
For certain intricate shapes, it has been proposed to use molds produced from granulated and bonded glass. Also, chemically machinable, glass-ceramic materials have been proposed as mold materials. Such molds are also removed mechanically.
The concept of readily removable mold materials, particularly core materials, is embodied in the lost wax process. In that process, for example, a solid wax core is formed as a base upon which to build a mold shape. Once the mold shape is formed, the wax is melted and removed. This procedure, of course, does not directly provide a mold, nor does it provide a mold that is readily soluble.
Recently, a technique has been proposed for forming glass bodies having a pristine surface that is free from mold marks. This technique involves molding the desired glass body with a surface layer of a relatively soluble glass. This soluble glass layer receives any mold marks, or other imperfections, and is dissolved away to leave the desired surface. The procedure, as well as families of soluble glasses for use in the procedure, are disclosed in U.S. Pat. Nos. 5,100,452 (Dumbaugh, Jr.) and 4,102,664 (Dumbaugh, Jr.). While this procedure is very useful for its purpose, it is apparent that it does not produce a cellulated body, and could not function to provide mold materials for casting purposes.
My co-pending application, Ser. No. 07/630,544, filed Dec. 20, 1990, now abandoned and refiled on Jul. 1, 1993 as Ser. No. 08/086,515, discloses an amorphous, polymeric material that contains phosphorous, aluminum and carbon atoms. This material may be thermally foamed at relatively low temperatures on the order of 300.degree. C. to produce a crystallized matrix having gas-filled, or vacuum-filled, cells dispersed throughout the matrix. The matrix may be essentially an aluminophosphate crystal phase or a mixture of alumino and borophosphate crystal phases.
A second co-pending application of mine, Ser. No. 07/732,906, filed Jul. 19, 1991 as a continuation-in-part of Ser. No. 07/630,813, filed Dec. 20, 1990, discloses a refractory body assembly. This assembly includes a barrier layer in an intermediate space between a refractory container and a honeycomb-type, refractory body positioned within the container. The barrier layer is a rigid, cellulated layer produced from the foamable material of the first mentioned application. There is no suggestion in these applications that the cellulated materials might be solubilized, or of the disclosed materials being suitable for use as mold materials.
It would be desirable to provide a light weight mold composed of a cellulated material capable of withstanding elevated temperatures such as encountered in casting processes. Such a material would be particularly useful if it could be readily removed, for example, following the casting process. This would greatly facilitate casting of regular shapes, as well as shapes having intricate designs. It is a basic purpose of the present invention to provide such desirable cellulated bodies, and mixtures adapted to their production.